An air filter designed to remove particulate is generally a device composed of fibrous materials. These fibrous materials may remove solid particulates such as dust, pollen, mold, and bacteria from the air. Air filters are used in applications where air quality is important, notably in building ventilation systems and in engines.
Air filters may be used in automobiles, trucks, tractors, locomotives and other vehicles that use internal combustion engines. Air filters may be used with gasoline engines, diesel engines, or other engines that run on fossil fuels or other combustible substances. Air filters may be used with engines in which combustion is intermittent, such as four-stroke and two-stroke piston engines, as well as other types of engines that take in air so that a combustible substance may be burned. For example, air filters may be used with some gas turbines. Filters may also be used with air compressors or in other devices that take in air.
Filters may be made from pleated paper, foam, cotton, spun fiberglass, or other known filter materials. Generally the air intakes of internal combustion engines and compressors tend to use either: paper, foam, or cotton filters. Some filters use an oil bath. Air filters for internal combustion engines prevent abrasive particulate matter from entering the engine's cylinders, where it would cause mechanical wear and oil contamination. In many fuel injected engines, a flat panel pleated paper filter element may be used. This filter is usually placed inside a plastic box connected to the throttle body with ductwork. Vehicles that use carburetors or throttle body fuel injection typically use a cylindrical air filter positioned above the carburetor or throttle body.
Air filters may also be used to filter cabin air, for example, air within a vehicle such as a car, truck, airplane, bus, train, tractor, etc. These air filters may typically be a pleated-paper filter in which outside-air is passed through the filters before entering the vehicle's passenger compartment. Some of these filters are rectangular and similar in shape to the combustion air filter.